Several devices for stacking and holding lumber to keep it from twisting and bending have been developed. The problem is particularly acute with green lumber which has recently been cut and has a high water content. Once a board has become twisted or bent, it is difficult or impossible to use. Losses of 20-30% of the boards in a stack of lumber to twisting or bending are not uncommon. The solution is to hold the stack of lumber or to lay the boards in special racks so they cannot twist or bend. Then as they dry, they dry straight.
U.S. Pat. No. 2,181,356 describes the problem and shows a rack for storing piled lumber at an angle in order to minimize the "crooking, splitting, bowing, checking, and cupping" of the lumber as it dries. A reduction in the loss of lumber to these factors from 20% to 1% is claimed. One problem with the rack is that the boards must be carefully inserted into the rack one at a time which is time consuming and expensive. The lumber comes from the sawmill in rectangular stacks with the boards laid horizontally. If the rack is to be used, the stacks must be broken down and the boards inserted into the rack individually. Another problem with the rack is that each different size of lumber requires different notched base supports in order to hold the boards at the proper angle. The rack in U.S. Pat. No. 2,247,519 also holds the lumber at an angle in order to use the force of gravity to hold each board both vertically and horizontally to keep it straight.
U.S. Pat. No. 3,504,404 discloses a device for holding stacked lumber in place during movement of the stack for shipment and could be used to hold lumber during storage as it dries although access would be awkward requiring removal of a top chain or beam. A somewhat similar arrangement is shown in U.S. Pat. No. 4,107,958 which is designed to protect large sheets of building materials from theft by the use of side clamps. U.S. Pat. No. 4,730,734 discloses another clamping device for protecting building materials or other goods from theft. The horizontal clamping bars are held on a vertical column which keeps them out of the way of the lumber or other goods when they are lifted.
None of the prior art rack devices provides retention of a unit stack of lumber to keep the boards straight. None of the prior art clamping devices provides easy application to a stack of lumber while allowing quick access to the lumber when lifted.